1. Field of the Invention
The present invention relates to a method for preparing a dried protein preparation.
2. Description of the Prior Art
The preparation of protein powders can for example be achieved by means of spray drying. Spray drying can be effected with starting solutions with protein contents in the range 5-20% (w/w). Protein solutions are frequently processed and atomised at these concentrations as their viscosity properties (0.1-0.5 Pa·s (at a shear rate of 100 s−1 at 70° C. (Physica UDS200 rheometer, DIN double gap Z1 geometry) mean that they are easily handled and pumped through standard processing equipment. Spray drying of solutions at the lower end of this protein concentration range can result in high levels of dusting (dust formation), which can result in reduced yields and increased risk of dust explosions. An additional disadvantage of spray drying powders can be the poor wettability and dispersibility properties of the dried powders, which have a low density and tend to float on the surface of water-based liquids.
Powders produced by roller drying are characterized by higher densities and improved wetting and dispersing properties. However, these protein powders have a less favourable taste profile, and have a darker colour than their spray dried equivalents. These defects can be ascribed to the high protein concentration (around 40%) needed for an efficient roller drying process.
Lowering the solids or protein concentration in the roller drying process to e.g. 20% (like in spray drying) would solve this problem. However, protein solutions in the 5-20% (w/w) concentration range do not lend themselves to roller drying. They become too fluid when applied to steam heated rollers and spread to form too thin a film, which burns onto the roller. The resulting film cannot be removed efficiently from the roller as a continuous film by the knives used for this purpose, but the protein is rather removed as scorched dust. Alternatively, a double (twin) roller dryer type can be used in which the protein solution subject to drying is contained in a “pool” between the two roller drums. However, the long residence time in this pool at elevated temperatures causes similar defects to the protein (browning) as observed in a high solids single drum dryer process. Additionally, under these conditions the formation of lysinoalanine (LAL) may be favored, which is not desirable.